1. Field of the Invention
This invention relates to fluid separation membranes. In another aspect, the invention relates to a fluid separation module.
2. Prior Art
It is known to separate one fluid from a mixture of fluids by using a membrane which is more permeable to the one fluid than the others of the mixture. The fluid mixtures are brought into contact with one side of the membrane, with a pressure differential being maintained across the membrane, and the permeable fluid will permeate the membrane to the other side thereof and thereby become separated from the fluid mixture.
The rate of permeation of the fluid through a membrane is a function of the difference in partial pressures of the fluid on opposite sides of the membrane. If these partial pressures are the same, none of the fluid will permeate the membrane. This presents a real problem when it is desired to treat a fluid mixture containing only very small amounts of the fluid to be separated from the mixture. For example, when it is desired to dehydrate ethanol containing one to two percent water, the permeation of only a small portion of the water will result in a water vapor partial pressure on the permeate side of the membrane equivalent to that on the feed side, so that no more water will permeate the membrane. One method of solving this problem is to use a sweep fluid which carries the permeated fluid away from the permeate side of the membrane to allow more of such fluid to permeate the membrane.
U.S. Pat. No. 3,536,611 discloses a membrane device which uses a sweep stream to sweep a permeated fluid from a bundle of membrane tubes through which the fluid has permeated. The sweep streams are brought in from opposite ends of the bundle of tubes and it is obvious that exterior piping, valves, etc. are required for directing the sweep streams into the device.
U.S. Pat. No. 3,499,062 discloses fluid separation apparatus in which part of a feed stream to be treated is passed through a membrane separator for sweeping out fluids which permeate the membranes of the separator. The least complicated embodiment of this apparatus is shown in FIGS. 6 and 9. Various piping and valves are used for directing the sweep stream into the separation apparatus. Such piping and valving, which must be used with any of the known separation apparatus where a sweep fluid is required, add to the cost and complexity of the system.